A significant challenge in modern research in many fields is the need for miniaturization and increased speed in the performance of biological assays without any loss in the level of quality and accuracy.
Biological assays have been performed using colorimetric techniques requiring the addition of one or more reagents to form a measurable reaction product which is monitored.
In some assays, relying on a single sample analysis, more than one analyte must be measured simultaneously to provide a meaningful result. Examples of such assays involve the determination of glucose and cholesterol content in a blood plasma sample. In other assays, it is necessary to quantify the behavior of a cell population as it is exposed to a chemical stimulus. An example of such an assay involves monitoring the change in intracellular calcium levels upon repeated exposure to a drug substance. Such an assay employs a fluorescent calcium marker agent to indicate intracellular calcium levels.
Assay conditions for one analyte often differ from those of another, and may further employ reagents that are incompatible with each other. Thus, individual assays can rarely be conducted for multiple analytes simultaneously in the same reaction phase, but rather must be conducted in parallel in independent experiments.
Prior art techniques have aimed, by varied and often complex means, to parallize protocols in biological assays and to increase the speed at which such assays can be conducted. This quest for speed and parallelization has generally involved the need to miniaturize the instruments used with such assays to account for a lower reagent requirements and shorter transport paths.
In some assays, different analytes in a sample can only be determined after some separation is performed. Liquid chromatographic and in recent years electrophoretic separations in tubes or microfabricated channels have been used as separation techniques.
Microfluidic devices have been fabricated in recent years to address many of the issues raised by the increased throughput demands of biological assays. The development of these devices has been the beneficiary of advancements in microfabrication technology originally applied in the electronics and semiconductor industries. Technologies that include photolithography, wet chemical etching and even injection molding of polymers have been applied in the fabrication of microscale channels and wells that form the conduit networks of microfluidic flow cells used in many assays. However, though microfluidic devices have increased throughput by decreasing sample and reagent requirements and reducing flow path and component size, they remain largely devices that perform the analysis of one sample at a time and are not amenable to simultaneous multi-sample analysis.
In order to allow for conducting simultaneous multi-sample analyses in a single assay format, it would therefore be desirable to provide methods and apparatus that are not limited to single sequential analyses. The present invention meets these and other needs.